This disclosure relates to organic thin film transistor (OTFT) array panels for display devices and to methods for making them.
Flat panel display devices, such as liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, electrophoretic displays, and the like, generally include a plurality of pairs of electrical field generating electrodes with an electro-optically active layer interposed therebetween. A LCD includes a layer of a liquid crystal material as the electro-optically active layer, and an OLED display includes an organic light emission layer as the electro-optically active layer.
Generally, one of the pair of electrical field generating electrodes is connected to a switching element, which provides it with an electrical signal, and the electro-optical active layer converts the electrical signal into an optical signal that enables the display of an image. Flat panel displays use TFTs, which are three-terminal elements, as the switching elements, and include gate lines for transmitting scan signals for controlling the TFTs, and data lines for transmitting image data signals to be applied to pixel electrodes.
Currently, organic TFTs (OTFTs), which include an organic semiconductor instead of inorganic semiconductor, such as silicon (Si), are being actively researched. Because the OTFT can be formed in either a fiber or a film type, in terms of the characteristics of the organic material, OTFTs are receiving much attention as a core element of a flexible display device. Also, because OTFTs can be fabricated by a solution process, such as ink jet printing, they can be applied relatively easily to large-scale flat panel display devices, the manufacture of which is limited only in terms of the deposition processes used for their application.
However, compared to inorganic semiconductors, organic semiconductors have relatively low heat and chemical resistances, so they can be easily damaged in the follow-up processes subsequent to their deposition. In addition, when source and drain electrodes are made of a low-resistance conductor, such as aluminum, a Schottky barrier is formed between the organic semiconductor and the source and drain electrodes, which can degrade the characteristics of the TFTs.
As a result, in order to protect the organic semiconductor materials and prevent the degradation of the OTFT characteristics, structures that include more stacks and corresponding additional processes are required. This, in turn, results in an increase in the number of masks required during manufacturing and a concomitant increase in manufacturing cost.